In a process of manufacturing a semiconductor device, various gases are used in a process performed on a semiconductor substrate under a reduced pressure. Conventionally, in a decompression processing apparatus using a vacuum chamber, more particularly, a plasma processing apparatus, a combustible gas and a combustion supporting gas may be simultaneously or alternately supplied into the same chamber. In such a case, preventing explosion of an exhaust gas in advance at the outlet side of a vacuum pump that evacuates the inside of a chamber has become one of the problems to be solved.
For example, in a plasma CVD apparatus, after a film is formed on a semiconductor substrate through a plasma CVD method using a combustible raw material gas in a chamber, plasma cleaning for removing deposits adhered to an inner wall of the chamber with plasma of a combustion supporting gas may be performed every time or periodically. In this case, when some of the combustible gas used in the film forming processing remains unreacted in the chamber and is mixed with the combustion supporting gas and discharged from the chamber during the immediately following plasma cleaning, a high-pressure or high-concentration exhaust gas may cause explosion (rapid pressure variation through combustion) at the outlet side of a vacuum pump due to, for example, generation of static electricity. In general, a detoxifying device is connected to the outlet side of the vacuum pump used in the plasma processing apparatus through an exhaust pipe. Since a vacuum pipe which is poor in strength and pressure resistance is used as this kind of exhaust pipe, the exhaust pipe may be easily damaged by the explosion of the exhaust gas so that an exhaust gas harmful to, for example, the human body or the environment may leak out to the outside.
In addition, a plasma etching apparatus also has a problem in that, when a dry etching is performed using a mixed gas composed of a combustible gas and a combustion supporting gas, a high-pressure or high-concentration exhaust gas containing the unreacted combustible gas and the combustion supporting gas may cause explosion at the outlet side of a vacuum pump, thus leaking out to the outside of an exhaust pipe.
Conventionally, a technology has been known in which, in order to prevent, in advance, explosion of an exhaust gas at the outlet side of a vacuum pump that evacuates the inside of a chamber of a decompression processing apparatus, an inert gas such as, for example, N2 gas is supplied to an exhaust pipe that connects the outlet side of the vacuum pump to an exhaust gas processing device such as, for example, a detoxifying device so as to dilute the exhaust gas (see, e.g., Japanese Patent Laid-Open Publication No. H9-000909 and Japanese Patent Laid-Open Publication No. 2012-038962).